Apparatus for removal of ions, and a method of manufacturing an apparatus for removal of ions from water

ABSTRACT

An apparatus and a method to remove ions from water. The apparatus includes a housing, an inlet to let water into the housing, an outlet to let water out of the housing, a first and second electrode connected to a power supply configured to create an electrical potential difference between the first and the second electrodes, and a spacer between the first and second electrodes to allow water to flow in between the first and second electrodes, the spacer comprising a pillar structure.

FIELD

The invention relates to an apparatus to remove ions.

BACKGROUND

In recent years one has become increasingly aware of the impact of humanactivities on the environment and the negative consequences this mayhave. Ways to reduce, reuse and recycle resources are becoming moreimportant. In particular, clean water is becoming a scarce commodity.Therefore, various methods and devices for purifying water have beenpublished.

A method for water purification is by capacitive deionization, using anapparatus having a flow through capacitor (FTC) to remove ions in water.The FTC functions as an electrically regenerable cell for capacitivedeionization. By charging electrodes, ions are removed from anelectrolyte and are held in an electric double layer at the electrodes.The electrodes can be (partially) electrically regenerated to desorbsuch previously removed ions without adding chemicals.

The apparatus to remove ions comprises one or more pairs of spaced apartelectrodes (a cathode and an anode) and may comprise a spacer, thespacer separating the electrodes and allowing water to flow between theelectrodes.

The apparatus comprises a housing comprising a water inlet to let waterin the housing and a water outlet to let water out of the housing. Inthe housing of the apparatus, the layers of electrodes (and spacers) arestacked in a “sandwich” fashion by compressive force, normally bymechanical fastening.

SUMMARY

The efficiency of the apparatus during purification is significantbecause it is indicative of the amount of water that may be purified bythe apparatus over a period of time.

It is desirable, for example, to improve the efficiency of the apparatusto remove ions.

According to an embodiment of the invention, there is provided anapparatus to remove ions from water, the apparatus comprising:

a housing;

an inlet to let water into the housing;

an outlet to let water out of the housing;

a first and second electrode connected to a power controller configuredto apply an electrical potential difference between the first and thesecond electrodes; and

a spacer between the first and second electrodes to allow water to flowin between the first and second electrodes, the spacer comprising apillar structure.

According to a further embodiment of the invention, there is provided amethod of manufacturing an apparatus to remove ions from water, themethod comprising:

providing a first electrode;

providing a spacer comprising a pillar structure to the first electrode;and

providing a second electrode to the spacer.

According to a further embodiment, there is provided an apparatus toremove ions from water, the apparatus comprising:

a housing;

an inlet to let water into the housing;

an outlet to let water out of the housing;

a first and second electrode connected to a power controller configuredto apply an electrical potential difference between the first and thesecond electrodes; and

a spacer between the first and second electrodes to allow water to flowin between the first and second electrodes, the spacer comprising ahelical structure.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will be described, by way of example only,with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 shows a schematic representation of an embodiment of an electrodefor use in an embodiment of the invention;

FIG. 2 shows a schematic representation of a stack of electrodes for usein an embodiment of the invention;

FIG. 3 shows a schematic representation of an apparatus to remove ionsfor use in an embodiment of the invention;

FIG. 4 shows schematically the ion concentration between two electrodes;

FIGS. 5 a-c show schematic cross-sections of a part of an apparatus toremove ions according to an embodiment of the invention;

FIG. 6 shows a schematic cross-section of two spacers;

FIG. 7 shows a schematic arrangement of an apparatus to remove ions foruse in an embodiment of the invention;

FIGS. 8 a to 8 c show apparatus to remove ions according to anembodiment of the invention; and

FIGS. 9 a to 9 e show apparatus to remove ions according to anembodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a schematic cross section of an embodiment of an electrode,being a first or a second electrode. In this example, the electrode 11has a sheet like shape with a rectangular form, but other shapes, suchas a round, polygonal or hexagonal shape are possible. In the electrodea hole 12 is provided, which may have a rectangular shape or anothershape, such as a round shape. When electrode 11 is in use, water may beflowing along the electrode from the outer edge(s) towards the hole, asis indicated by the dotted arrows 13 in FIG. 1. Typically, the outerdimensions of the electrode 11 are about 16×16 cm and the dimensions ofthe hole 12 are about 3×3 cm.

An advantage of a rectangular or a hexagonal shape of the electrode maybe that this type of electrode may be efficiently produced with respectto use of material. An advantage of a round shaped electrode with around hole in the center may be that distance between the outer edge andthe inner edge (i.e. the distance the water will flow along theelectrode) is substantially constant for all flow directions.

FIG. 2 shows a stack of electrodes. The first electrodes 21 and thesecond electrodes 22 each comprises a current collector, indicated by 34in FIG. 3, and an ion storage material, indicated by 35 in FIG. 3. Thecurrent collector is connected to a power controller PC configured toapply an electrical potential difference between two adjacentelectrodes. The ion storage material may store ions that have beenremoved from the water. The ion storage material may be a so-called highsurface area material with more than 500 m²/gr, more than 1000 m²/gr, ormore than 2000 m²/gr. The material may comprise activated carbon, carbonaerogel, graphene, carbon nanofiber and/or carbon nanotube on both sidesof the electrode which are in contact with the water.

FIG. 3 shows a schematic representation of an apparatus to remove ionsfor use with an embodiment of the invention. The apparatus has a housing31 comprising a water inlet 32 and a water outlet 33. During ion removalfrom the water, the water will flow from the inlet 31 to the outlet 33through the flow through capacitor (FTC), comprising a pair of a firstelectrode 21 and an adjacent second electrode 22. The flow of water isindicated by the dotted arrows.

Between two adjacent electrodes a spacer 36 may be provided. The spacer36 may have a shape as is depicted in FIG. 1. A main function of aspacer is to separate the first electrode from the second electrode, forexample by maintaining a substantially constant or fixed distancebetween the two electrodes.

By applying an electrical potential difference between the first andsecond electrodes by a power controller PC, for example by applying apositive voltage to the first electrode (the anode) 21 relative to thesecond electrode (the cathode) 22, the anions of the water flowingthrough the spacer 36 are attracted to the first electrode 21 and thecations are attracted to the second electrode 22. In this way the ions(anions and cations) will be removed from the water flowing through thespacer 36.

To increase the ion removal efficiency of the apparatus, the electrodesmay have a charge barrier, for example an ion exchange membrane or anion selective membrane. For example, the membrane provided on or to thecathode may be permeable for cations and only substantially allow thetransport of cations and substantially block the transport of anions andthe membrane provided on or to the anode may be permeable for anions andsubstantially block the transport of cations.

The electrical potential difference between the anode and the cathode israther low, for example lower than 2 Volts, lower than 1.7 Volts orlower than 1.4 Volts. A power controller is used to control theconversion of the voltage and electrical current from a power supply tothe desired voltage difference over the first and second electrodes.

An element of the efficiency of the apparatus is the ion flux, where theion flux may be defined as the number of ions removed from the water,for example from the water in a spacer, to one of the electrodes perunit time per projected electrode area.

FIG. 4 shows two adjacent electrodes in an apparatus to remove ions. Thedotted line 41 indicates the concentration of ions in the water flowingbetween the two electrodes. As can be seen in FIG. 4, near the surfaceof electrodes the ion concentration is lower than in the center. Forexample, the ion concentration in the water in region 42 may be lowerthan the ion concentration in region 43. Although in FIG. 4 only tworegions are depicted, it should be understood that the ion concentrationmay decrease gradually or even linearly with the distance from one ofthe electrodes and that therefore the choice of regions is arbitrary.Where ion exchange membranes or ion selective membranes are used, whichare placed between the electrode and the spacer, a similar situation mayoccur, where the ion concentration in the water in region 42 may belower than the ion concentration in region 43.

A low ion concentration close to the electrode (or membrane) may resultin a low ion flux to the electrode (or through the membrane) to theelectrode. By increasing the ion concentration close to the electrode(or the membrane) the ion flux may be increased, hence improving ionremoval efficiency. The ion concentration near the electrodes may beincreased for example by mixing the water, by the displacement of thewater in a substantially direction perpendicular to electrodes or byincreasing the mobility of the ions in the water.

According to an embodiment, the ion improvement device comprises amixing device. The mixing device may be a spacer with a specialstructure that causes mixing of the water and which may even causeturbulence in the water. The spacer may have a spiral or a helicalstructure.

A helical spacer may influence the water flow by forcing the fluid totwist along the spacer. The effect may be a faster local velocity of thewater or it may result in that water with higher ion concentrationfurther away from the electrode (or membrane) is brought closer to theelectrode (or membrane), which may increase the ion flux towards theelectrode. A helical spacer may improve the ion flux by a factor up totwo times compared to a non-helical spacer. Furthermore, a helicalspacer may increase the mixing of the water where the flow is stilllaminar. A helical spacer may promote turbulence in the flow channel,which may further improve the mixing of the water.

According to a further embodiment, the mixing device causes an unsteadyflow in the water. In an unsteady flow, the flow profile is notconstant, i.e. it changes over time. For example the flow velocity at acertain point may change over time and/or its direction.

Additionally or alternatively, the ion flux improvement device maycomprise a turbulence creator to create a turbulent flow in the water inthe spacer or a recirculation circuit with a pump and a storagefacility. In the storage facility, water from the FTC with low ionconcentration may be mixed with water in the storage facility with ahigher ion concentration. The storage water may be used for otherpurposes, for example as a swimming pool, or for irrigation.

According to an embodiment the ion flux improvement device comprises aspacer, which is ion-conductive or comprises ion-conductive material. Anion-conductive spacer may improve the ion mobility towards one of theelectrodes. An ion-conductive spacer may comprise a membrane (forexample: anion exchange membrane, cation exchange membrane, a mosaicmembrane (for mixed charges) and/or a bipolar membrane) or an ionexchange resin (for example anion exchange resin, cation exchange resinor mixed ion exchange resin). An ion-conductive spacer allows thepassage of charged species such as ions and may increase the mobility ofthe ions towards one of the electrodes.

FIG. 5 a shows a schematic cross section of a first and a secondelectrode, between which water is flowing. The elements in FIG. 5, suchas electrodes 21 and 22 and their sizes and mutual distances aredepicted schematically. It may be that the flow of water through thespacer is more or less laminar, e.g. the water flows in more or lessconstant layers (parallel to the electrodes) without mixing of the wateror without water flowing with a direction component perpendicular to theelectrodes. In region 61 the flow velocity of a laminar flow parallel tothe electrodes is depicted, wherein the length of the straight arrowsindicates the velocity of the flow: a longer arrow indicates a highervelocity.

According to an embodiment, the ion improvement device may comprise avelocity adjuster 64 configured to adjust a flow velocity of a firstportion of the water with respect to a second portion of the water,wherein, in use i.e. during ion removal from the water, in the firstportion an ion concentration is higher than in the second portion. If aportion of water experiences the electrical potential difference for alonger period of time (i.e. its flow velocity is lower) than anotherportion of water, then at the same ion concentration in the water thenumber of ions removed from this portion will be higher than fromanother portion of water that experiences the electrical potentialdifference for a shorter period of time.

Velocity adjuster 64 may be located in the spacer, along the spacer, oroutside the spacer or it may be incorporated in the spacer. Without thevelocity adjuster 64 the flow in the flow channel will follow aparabolic (“Poisseuille”) profile with a maximum flow velocity in thecenter of the flow channel and zero flow at both electrode surfaces. Thevelocity adjuster 64 is constructed to change the velocity of the waterin such a way, that a portion of the water flowing further away from oneof the electrodes (for example in region 63) is flowing slower relativeto a portion flowing closer to one of the electrodes (for example inregion 62). Region 65 depicts a possible effect on the flow velocity ofthe water, wherein the length of the straight arrows indicates theabsolute velocity of the flow: a longer arrow indicates a highervelocity and the orientation of the arrow indicates the direction of theflow. In FIG. 5 a situation is depicted where the velocity adjuster 64has reduced the velocity of the water so much that the velocity in thecenter of the flow channel has become lower than closer to theelectrodes. Nevertheless, in another embodiment of the velocity adjuster64, a lower reduction of the flow velocity in the center may beachieved, where the flow will only gradually decrease from the center toclose to the electrodes. In another embodiment the velocity adjuster maycause the velocity to be more uniform inside the spacer, where the flowvelocity will be substantially independent from the distance from theelectrode.

The velocity adjuster 64 may comprise a porous material, wherein theflow resistance in the center of the velocity adjuster is larger than inone or more edges, causing the velocity of the water passing through thecenter of the velocity adjuster 64 (for example in region 63) to bereduced compared to the water passing through the edge of the velocityadjuster 64 (for example in region 62). The flow resistance of thisvelocity adjuster may be continuously increasing from an edge, near oneof the electrodes, towards the center of the velocity adjuster, i.e. thecentral axis of the spacer. For example, the porosity of the velocityadjuster 64 may be varied from a value larger than 70%, larger than 80%,or larger than 90% close to an electrode (e.g. region 62) to a value ofsmaller than 70%, smaller than 60% or smaller than 50% towards thecenter of the velocity adjuster (e.g. region 63). Porosity may bemeasured as a percentage of the volume of voids over the total volume.

The velocity adjuster 64 for use in the apparatus to remove ionsaccording to an embodiment of the invention may comprise a spacer withmultiple layers between the electrodes and the layer(s) close to theelectrode(s) may have a low flow resistance and the layer(s) furtheraway from the electrode(s) a relatively higher flow resistance. The lowflow resistance may cause a higher velocity of the water close to anelectrode and the higher flow resistance may cause a lower velocity ofthe water further away from the electrode. Without the velocity adjuster64 less ions will be removed from the water in the center of the flowchannel or spacer, because these ions will have to migrate over a largerdistance whereas the residence time of the ion in the center of the flowchannel or spacer is lower than that closer to an electrode. Since thewater further away from an electrode will be less easily de-ionized thanthe water closer to the electrode it is advantageous to have a lowervelocity to the water further away from the electrode so that the waterstays longer between the electrodes resulting in more time for theelectrodes to attract the ions. Water close to an electrode may berelatively quickly de-ionized because of the close proximity of theelectrode and therefore shorter migration distance for the ions and thiswater may therefore stay a relatively shorter time between theelectrodes. The layers in the spacer may comprise a porous material witha low flow resistance in a first direction and a higher flow resistancein a second direction. This may be achieved by orienting fibers in thespacer substantially parallel to the first direction and/orperpendicular to the second direction. The layer in the spacer close toan electrode may be oriented such that the first direction issubstantially equal to the water flow direction. The water may thereforeexperience a low flow resistance close to the electrode and the speed ofthe water may therefore be relatively high. A layer in the spacerfurther away from the electrode is oriented such that the seconddirection is substantially equal to the water flow direction so that thewater further away from the electrode experiences a higher resistivityresulting in a lower velocity of the water. The thickness of the spacerwith the velocity adjuster may be 20-300 micrometers, 40-200micrometers, 60-150 micrometers or 70-120 micrometers.

A further example of a velocity adjuster comprises a material thatcloses off the spacer but has several small channels in the longitudinaldirection of the spacer through which water may pass from one side tothe other. The overall cross-section of the channels in the region nearan edge may be larger than the overall cross-section of the channels inthe central region of the velocity adjuster 64.

FIG. 5 b is an example of such a velocity adjuster 64 for use in anapparatus to remove ions according to an embodiment of the invention.The velocity adjuster 64 has channel walls creating small channels 67,68 in the spacer 64. The channel walls are permeable for water and/orions flowing through them but they create a resistivity for the waterflow. As depicted the channel walls are substantially parallel to theelectrodes but they may be more randomly oriented. A small channel 68 inthe middle of the spacer creates a higher flow resistivity than a largersmall channel 67 closer to an electrode. The flow velocity of the waterflowing in the flow direction substantially parallel to the channelwalls is thereby adjusted so that the flow velocity is lower in themiddle of the spacer than the flow velocity closer to the electrodes 21,22. The flow resistance of the small channels may be continuouslyincreasing from a larger small channel 67 near the edge, near one of theelectrodes 21, 22, towards the middle, i.e. the central small channel 68of the spacer. The water further away of an electrode may get a lowervelocity so that it stays longer between the electrodes and there ismore time by the electrodes 21, 22 to attract the ions. Water close toan electrode may be relatively quickly de-ionized because of the closeproximity of the electrode and may therefore be for a relatively shorttime between the electrodes. The water further away from the electrodemay because of the higher flow resistance further away from theelectrode also be moved towards an electrode so that the ions are moreeasily attracted to an electrode.

FIG. 5 c discloses a cross-section of the velocity adjuster 64 of FIG. 5b perpendicular to the flow direction. FIG. 5 c discloses that the smallchannels have a total cross section which is decreasing close to thecenter 68 of the flow channel and which is increasing closer 67 to theelectrodes 21, 22.

Another example of a velocity adjuster may be a shifted spacer, as isdepicted in FIG. 6. The spacer may comprise a grid structure 71. Thegrid structure will influence the velocity of the water flowing throughthe spacer. It may also cause mixing of the water or cause adisplacement of the water in a direction perpendicular to electrodes. Byshifting or rotating the orientation of the grid with respect to theelectrode, these effects may be further optimized. FIG. 6 shows ashifted grid structure 72. The shift or rotation of the orientation maybe around 45 degrees, where the threads of the spacer are at an angle ofaround 45 degrees with respect to the side of one of the electrodes, ascan be seen from FIG. 6. Or in other words, the threads of the spacerare substantially parallel to the diagonal of the electrode. Note thatthe dimensions of the spacer are about the same as the dimension of theelectrode shown in FIG. 1 or may be a bit larger, for example 17×17 cm.

FIG. 7 shows another embodiment of an ion flux improvement device,comprising an electrical current measurement device A and a flowcontroller FC. The current measurement device A measures the currentflowing to the first electrode 21 or to the second electrode 22. The ionflux is a function of the electrical current and the electrical currentmay thus be used as a measure for the ion flux. The current measurementdevice A provides a current signal to the flow controller FC, which mayadjust the water flow depending on the measured electrical current. Theflow controller FC may be configured to adjust the flow velocity of thewater, for example by controlling the pump P, via a control signal. Inthis way, the ion flux may be controlled via the flow controller.

By increasing the flow velocity, the ion flux may increase to one of theelectrodes (or to the ion exchange membrane or ion selective membrane),because of an increased ion concentration nearby, for example in region42 in FIG. 4.

However, at a high flow velocity, a further increase of the flow may notresult in an increased ion flux. An optimum ion flux to the electrode(or membrane) may be obtained when the percentage of ions removed fromthe water per cycle is relatively low, for example below 80%, below 60%,below 40% or below 20%. In one cycle the water flows once between twoFTC electrodes.

A high ion flux may thus be obtained for example at a flow velocityhigher than 1 liter/m² projected electrode area/min, or higher than 2liters/m² projected electrode area/min or even higher than 3 liters/m²projected electrode area/min or even higher than 4 liters/m² projectedelectrode area/min.

Although increasing the flow velocity may cause the number of ions orpercentage of ions removed from the water per cycle to be lower, the ionflux, which is defined per unit time per projected electrode area, mayincrease because the number of cycles per unit time may also increasewith higher flow velocity.

In an embodiment, the ion flux improvement devices may comprise adeionization rate measurement device to measure the deionization rate(i.e. the percentage of ions removed from the water) per cycle. Thedeionization rate measurement device may comprise two ion concentrationmeasurement devices, one measuring the ion concentration of the waterbefore the water flows between the electrodes and one measuring the ionconcentration of the water after flowing between the electrodes. Thedeionization rate measurement device may comprise only one of these twoion concentration measurement devices and an electrical currentmeasurement device as described above. The deionization rate measurementdevice may calculate the deionization rate on the basis of onemeasurement of the ion concentration and the measurement of the currentflowing to one of the electrodes. The deionization rate measurementdevice may provide a deionization rate signal indicating the measured orcalculated deionization rate.

The ion flux improvement device may further comprise a flow controllerto control the water flow in response to the deionization rate signal.In this way, it is possible to (automatically) maintain a certaindeionization rate per cycle by adjusting the flow velocity, for examplea deionization rate per cycle below 20%, where only up to 20% of theions in the water are removed per cycle. It is possible to increase thepercentage of ion removal per cycle, for example from 20% in the firstcycle to 40% in the second cycle to 60% in the third cycle and to 80% inthe fourth cycle and effectively almost complete removal in the fifthcycle.

Using the above mentioned device to remove salt from water, the ion fluxmay be higher than 0.5 grams salt per m² projected electrode area permin, higher than 1.0 gram salt per m² projected electrode area per min,higher than 1.5 grams salt per m² projected electrode area per min orhigher than 2.0 grams salt per m² projected electrode area per min.

Increasing the flow velocity may cause the flow regime to change from alaminar flow to an unsteady or turbulent flow. In the laminar regime thepressure drop shows a linear relationship with the flow velocity.However, in an unsteady or turbulent regime, the pressure drop over thespacer or flow channel is no longer linear with the flow velocity, butincreases more rapidly with the flow. This involves more pumping energy.To prevent the flow from changing from laminar to (semi) turbulent flow,the pressure drop should be limited, for example in the range of 0-20bar per m² projected electrode area, in the range of 15-18 bar per m²projected electrode area or in the range of 2-10 bar per m² projectedelectrode area. The pressure drop may be limited to 0.1-20 bar per m²projected electrode area or 1-15 bar per m² projected electrode area.

FIG. 8 a discloses a cross-section of an apparatus to remove ionsaccording to a further embodiment of the invention comprising a firstand second electrode 21, 22 and a spacer between the first and secondelectrodes 21, 22. The spacer may have a helical structure 81. Thethickness of the spacer with the helical structure 81 may be 20-300micrometers, 40-200 micrometers, 60-150 micrometers or 70-120micrometers. The helical structure 81 may influence the principal waterflow 83 by forcing the fluid to twist along the helical structure in adirection 85. The effect may be a faster local velocity of the water orit may result in that water with a higher ion concentration further awayfrom the electrode (or membrane) may be brought closer to the electrode(or membrane), which may increase the ion flux towards the electrode. Ahelical structure in the spacer may improve the ion flux by a factor upto two times compared to a spacer without a helical structure.Furthermore, a helical structure may increase the mixing of the waterwhere the flow is still laminar. A helical structure may promoteturbulence in the flow channel, which may further improve the mixing ofthe water. The electrodes may comprise a flat surface and multiplehelical structures may be sandwiched between the flat surface of thefirst electrode and the flat surface of the second electrode. One of thefunctions of the spacer is to keep the surfaces of the two electrodes ata substantial constant distance of, for example, between 0.02 and 0.5mm. This is significant because if the distance between the electrodesis irregular then this may affect the flux of ions towards theelectrode, with lower fluxes where the spacer is thicker. The helicalstructure 81 may provide seven twists over the length of the helicalstructure. Seven twists would assure that the water is flowing alongeach electrode at least seven times. The porosity of the spacer with thehelical structure may be larger than 50%, larger than 60%, larger than70% or larger than 80%.

FIG. 8 b discloses a cross-section of an apparatus to remove ionsaccording to a further embodiment of the invention comprising a firstand second electrode 21, 22 and a spacer between the first and secondelectrodes 21, 22. The spacer has a helical structure 81 having a lesssteep torsion and only half a twist in total. An advantage may be thatthe flow resistance in such a case is lower and that the water willrotate along an electrode. An optimum between low flow resistance andsufficient interaction with the electrodes may be with a number oftwists between 0.5 and 7, between 1 and 5 or between 2 and 4.

FIG. 8 c discloses a cross-section of an apparatus to remove ionsaccording to a further embodiment of the invention. FIG. 8 c gives a topview of a spacer with one of the electrodes removed so that multipleadjacent helical structures 81 on top of the flat surface of theelectrode 22 can be seen. The helical structures have four and halftwists and the twists of two adjacent helical structures 81 areopposite. The helical structures 81 cause the water to twist 85 aroundthe principal flow direction 83 of the water and since two adjacenthelical structures 81 have an opposite twist the water in between thehelical structures 81 move in the same direction substantiallyperpendicular to the principal flow direction 83. This may improve theflow of the water towards an electrode at a position 89 in between thehelical structures 81. Since two adjacent helical structures areco-operating there may be a relatively low increase of the flowresistance.

The twist direction of two adjacent helical structures 81 may also bethe same which causes turbulence in between the helical structures andimproved mixing. The helical structures in FIG. 8 c have a support 87 inthe center. This forces the water out of the center of the helicalstructure towards the electrodes where the water is de-ionized.

Any embodiment of the above described apparatus to remove ions may beused for the removal of ions from water in a swimming pool, from waterin a storage tank or from water in a factory plant or from ground water.

FIG. 9 a discloses a cross-section of an apparatus to remove ionsaccording to a further embodiment of the invention comprising a firstand second electrode 21, 22 and a spacer between the first and secondelectrodes 21, 22. The spacer may have a structure as a pillar 91 tokeep the electrodes at a substantially fixed distance. The thickness ofthe spacer with the pillar structure may be 20-300 micrometers, 40-200micrometers, 60-150 micrometers or 70-120 micrometers. The pillarstructure 91 may be produced in a netting structure or framework 93 toform a layer which may form the spacer. The spacer is electricallyinsulating and at the same time open enough for water and ions to movethrough. The term pillar is to be interpreted as a structural elementthat keeps the first and second electrodes at a distance. The netting 93keeps the pillar 91 substantially perpendicular compared to the maindirection of the spacer. The netting framework causes a higher flowresistivity in the middle of the flow channel between the electrodes 21,22 thereby forcing the water in the flow channel to move closer to thefirst or second electrode resulting in increased de-ionization of water.The netting framework and the pillars may cause better mixing of thewater in the flow channel, which may increase the ion flux towards anelectrode. An advantage of the spacer comprising pillars and a nettingis that it creates a very open spacer (particularly in the flowdirection) with a low flow resistivity, which may result in a lowerpressure drop over the channel, or increased flow in the flow channeland it may also result in a reduced risk of fouling of the spacer. Theporosity of the spacer with the pillar structure may be larger than 50%,larger than 60%, larger than 70% or larger than 90%.

The electrodes may have a flat surface and multiple pillars held by thenetting may be sandwiched between the flat surface of the firstelectrode and the flat surface of the second electrode. One of thefunctions of the spacer is to keep the surfaces of the two electrodes ata substantially constant or fixed distance of, for example, between 0.02and 0.5 mm. This is significant because if the distance between theelectrodes is irregular, then the ion flux towards the electrodes may beaffected.

FIG. 9 b gives a top view of a part of a spacer with one of theelectrodes removed so that the multiple adjacent pillars 91 on top ofthe flat surface of the electrode 22 which are held in the netting 93can be seen. The netting 93 provides support over the full surface ofthe electrode so that it keeps the pillars 91 substantiallyperpendicular to the surface of the electrode as well as at asubstantially fixed distance with respect to each other.

FIG. 9 c discloses a cross-section of an apparatus to remove ionsaccording to a further embodiment of the invention. The pillar 95 inthis embodiment may comprise a spherical, elliptical or egg shape sothat the pillar structure may have a thicker middle portion so as toprovide for a higher flow resistivity in the middle of the flow channelin order to force the water flowing in the center part of the flowchannel between the electrodes 21, 22 in the direction of an electrode.At the same time the flow velocity in the center of the flow channel maybe reduced compared to that of the water flowing closer to the firstand/or second electrode. The pillar may have a conical or rhombusstructure, which is thicker in the middle than at an edge. The spacermay comprise a netting 97 to keep the pillars 95 in position. Thenetting of FIG. 9 c may be constructed similarly as the netting in FIG.9 b.

FIG. 9 d discloses a cross-section of an apparatus to remove ionsaccording to a further embodiment of the invention. This embodiment isthe same as the embodiment of FIG. 9 c except that the netting isomitted. The pillars 97 may be spherical, elliptical, conical, rhombusor ball shaped so as to provide a higher flow resistivity further awayfrom the electrode 21, 22 and hence increasing the residence time of thewater in the center of the channel compared to that of an edge of thespacer. The pillars 97 may be attached to the electrodes so that theelectrodes keep the pillars substantially perpendicular to the electrodesurface by, for example, a glue or a specific coating. The pillars mayalso be produced by printing the pillars on an electrode with, forexample, a 3D printer and subsequently providing another electrode ontop of the already printed electrode. The pillars may be printed on topof an additional layer, for example an ion exchange membrane, which maybe placed on top of the electrode as a separate layer or as a coating orlaminate.

FIG. 9 e discloses a cross-section of an apparatus to remove ionsaccording to a further embodiment of the invention. This embodiment isthe same as the embodiment of FIGS. 9 a and 9 b except that the nettingis omitted. The pillars 99 may be connected to the electrodes so thatthe electrodes keep the pillars substantially perpendicular to theelectrodes. The pillars may be produced by printing the pillars on anelectrode with, for example, a 3D printer.

An advantage of the pillars without a netting is that a very open spacermay be created in which the flow resistivity is reduced as well as therisk of fouling is reduced.

Furthermore, the description also explains how ions may be removed byproviding a method comprising: providing an electrical potentialdifference between a first and a second electrode in a housing; allowingwater to flow between the first and second electrodes from an inlet inthe housing to an outlet in the housing; and improving the ion flux fromthe water to the first and/or second electrode.

An apparatus to remove ions from water is described, the apparatus maycomprise a housing, an inlet to let water in the housing, an outlet tolet water out of the housing, a first and a second electrode connectedto a power controller configured to apply an electrical potentialdifference between the first and the second electrodes, and an ion fluximprovement device configured to improve the ion flux from the waterflowing between the first and second electrodes to one of the first andthe second electrode. The ion flux improvement device may comprise amixing device constructed and arranged to mix the water, or an unsteadyflow creator configured to create an unsteady flow in the water, or aturbulence creator configured to create turbulence in the water, or aspacer between the first and second electrodes configured to allow waterto flow in between the first and second electrodes, the spacer having aspiral structure to change a flow profile of the water. The mixingdevice may comprise a recirculation circuit constructed and arranged torecirculate water flowing between the first and second electrodes, therecirculation circuit may comprise a pump and a storage facility. Theion flux improvement device may comprise a spacer between the first andsecond electrodes to allow water to flow in between the first and secondelectrodes, the spacer may comprise ion-conductive material to increasea mobility of ions towards the first electrode or the second electrode.The ion flux improvement device may comprise a spacer between the firstand second electrodes to allow water to flow in between the first andsecond electrodes, the first and second electrodes and the spacer mayhave a substantially rectangular sheet-like shape, in which a hole maybe provided; and the spacer may comprise a grid structure and anorientation of the grid structure may be rotated with respect to astraight side of the first and second electrodes by at least 30 degrees,in the range of 30-50 degrees or about 45 degrees. The ion fluximprovement device may comprise a velocity adjuster constructed andarranged to adjust a flow velocity of a first portion of the water withrespect to a second portion of the water, wherein, in use, i.e. whenremoving ions from water, in the first portion an ion concentration ishigher than in the second portion. The ion flux improvement device maycomprise an electrical current measurement device arranged andconstructed to measure an electrical current between the first and thesecond electrodes and to provide a current signal indicating theelectrical current; and a flow controller arranged and constructed toreceive the current signal and adjust a flow velocity at which the wateris flowing between the first and second electrodes in response to thecurrent signal. The flux improvement device may comprise a deionizationrate measurement device arranged and constructed to measure adeionization rate per cycle of the water flowing between the first andthe second electrodes and provide a deionization rate signal indicatingthe deionization rate; and a flow controller arranged and constructed toreceive the deionization rate signal and adjust a flow velocity at whichthe water is flowing between the first and second electrodes in responseto the deionization rate signal. The flow controller may be arranged andconstructed to maintain the deionization rate below 60%, below 40% orbelow 20% of ions removed per cycle. Alternatively, the percentage ofion removal per cycle may be increased for example from 20% in the firstcycle to 40% in the second cycle to 60% in the third cycle and to 80% inthe fourth cycle and effectively almost complete removal in the fifthcycle. The flow controller may be arranged and constructed to maintainthe flow velocity higher than 2 liters/m² projected electrode area/min,higher than 3 liters/m² projected electrode area/min, or higher than 4liters/m² projected electrode area/min. The flow controller may beconstructed and arranged to provide a control signal to a pump, the pumpbeing constructed and arranged to receive the control signal and pumpthe water between the first and second electrodes with a flow velocityin response to the control signal.

Embodiments may also be provided in the following numbered clauses:

1. An apparatus to remove ions from water, the apparatus comprising:

a housing comprising:

-   -   an inlet to let water into the housing,    -   an outlet to let water out of the housing, and    -   a first and a second electrode connected to a power controller        configured to apply an electrical potential difference between        the first and the second electrodes;

a velocity adjuster constructed and arranged to adjust a flow velocityof a first portion of the water flowing between the first and secondelectrodes with respect to a second portion of the water flowing betweenthe first and second electrodes.

2. The apparatus according to clause 1, wherein the velocity adjuster isconstructed and arranged to adjust the flow velocity of the firstportion of the water to be reduced compared to the flow velocity of thesecond portion of the water.3. The apparatus according to clause 1 or clause 2, wherein the firstportion of the water is flowing further away from the first electrodeand/or the second electrode than the second portion of the water.4. The apparatus according to any of clauses 1-3, wherein the firstportion of the water is flowing through the center of the velocityadjuster.5. The apparatus according to any of clauses 1-4, wherein the secondportion of the water is flowing through an edge of the velocityadjuster.6. The apparatus according to any of clauses 1-5, wherein the secondportion of the water is flowing closer to the first electrode and/or thesecond electrode in the velocity adjuster.7. The apparatus according to any of clauses 1-6, wherein the velocityadjuster comprises a material with a flow resistance which may beadjusted to adjust the flow velocity of the water.8. The apparatus according to any of clauses 1-7, wherein the velocityadjuster comprises a porous material, wherein a flow resistance in thecenter of the velocity adjuster is larger than closer to an edge,causing the velocity of the water passing through the center of thevelocity adjuster to be reduced compared to the water passing throughthe edge of the velocity adjuster.9. The apparatus according to any of clauses 1-8, wherein the velocityadjuster comprises a porous material, where the porosity increases fromthe center of the velocity adjuster to the first electrode and/or thesecond electrode.10. The apparatus according to any of clauses 1-9, wherein the flowresistance of the velocity adjuster continuously increases from near thefirst electrode and/or the second electrode, towards the center of thevelocity adjuster.11. The apparatus according to any of clauses 1-10, wherein the velocityadjuster is provided along the spacer, outside the spacer orincorporated in the spacer.12. The apparatus according to any of clauses 1-11, wherein the velocityadjuster comprises a spacer having a grid structure which is shiftedand/or rotated with respect to the first electrode and/or the secondelectrode to adjust the velocity of the water flowing through thespacer.13. The apparatus according to any of clauses 1-12, wherein the velocityadjuster comprises a spacer with multiple layers between the first andsecond electrodes and a layer close to the first electrode and/or thesecond electrode has a low flow resistance and a layer further away fromthe first electrode and/or the second electrode has a relatively highflow resistance.14. The apparatus according to clause 13, wherein the layers comprise aporous material with a low flow resistance in a first direction and ahigher flow resistance in a second direction, where a layer close to thefirst electrode and/or the second electrode is oriented such that thefirst direction is substantially equal to the water flow direction.15. The apparatus according to clause 14, wherein a layer further awayfrom the first electrode and/or the second electrode is oriented suchthat the second direction is substantially equal to the water flowdirection.16. The apparatus according to clause 1, wherein the velocity adjustercomprises a material having small channels and the cross-section of achannel in a region closer to the first electrode and/or the secondelectrode may be larger than the cross-section of a channel in thecenter of the velocity adjuster.17. The apparatus according to clause 16, wherein the velocity adjustercomprises a material that closes off the spacer but has several smallchannels in the longitudinal direction of the spacer through which watermay pass from one side to the other and the total cross-section of thechannels in the region near an edge may be larger than the totalcross-section of the channels in a central region of the velocityadjuster.18. A method to remove ions, the method comprising:

providing an electrical potential difference between a first and thesecond electrode in a housing;

allowing water to flow between the first and second electrodes from aninlet of the housing to an outlet of the housing; and

adjusting a flow velocity of a first portion of the water with respectto a second portion of the water.

19. The method according to clause 18, wherein the flow velocity of thefirst portion of the water is lower than the flow velocity of the secondportion of the water and the first portion of the water is flowingfurther away from the first electrode and/or the second electrode thanthe second portion of the water.20. An apparatus to remove ions from water, the apparatus comprising:

a housing comprising:

-   -   an inlet to let water into the housing,    -   an outlet to let water out of the housing, and    -   a first and a second electrode connected to a power controller        configured to apply an electrical potential difference between        the first and the second electrodes;

a spacer between the first and second electrodes to allow water to flowin between the first and second electrodes, the spacer comprising ahelical structure.

21. The apparatus according to clause 20, wherein the first and secondelectrodes each comprise a substantially flat surface at a substantiallyconstant distance from each other.22. The apparatus according to clause 21, wherein the helical structureis sandwiched in between the flat surface of the first and secondelectrodes.23. The apparatus according to any of clauses 20-22, wherein the helicalstructure forces the water to twist along the helical structure.24. The apparatus according to any of clauses 20-23, wherein the helicalstructure forces the water further away from the first electrode and/orthe second electrode to a position closer to the first electrode and/orthe second electrode.25. The apparatus according to any of clauses 20-24, wherein the helicalstructure creates turbulence in between the first and second electrodesto improve mixing of water.26. The apparatus according to any of clauses 20-25, wherein the spacercomprises multiple helical structures.27. The apparatus according to any of clauses 20-26, wherein the spacercomprises multiple helical structures and the rotational direction ofadjacent helical structures is opposite.28. The apparatus according to any of clauses 20-27, wherein the waterflow through the spacer has a principal direction substantially parallelto the first electrode and/or the second electrode and the helicalstructure is oriented substantially parallel to the principal direction.29. The apparatus according to clause 28, wherein the helical structureforces the water to rotate in direction substantially perpendicular tothe principal direction.30. The apparatus according to clause 29, wherein two adjacent helicalstructures rotate the water in opposite direction.31. The apparatus according to clause 29, wherein two adjacent helicalstructures rotate the water in the same direction.32. The apparatus according to any of clauses 20-31, wherein the helicalstructure comprises a support in the center of the helical structure.33. A method to remove ions, the method comprising:

-   -   providing an electrical potential difference between a first and        the second electrode in a housing;    -   allowing water to flow between the first and the second        electrodes from an inlet of the housing to an outlet of the        housing;    -   forcing the water to rotate in a rotational direction around a        principal axis substantially parallel to the first electrode        and/or the second electrode; and    -   improving the ion flux from the water to the first electrode        and/or the second electrode.        34. An apparatus to remove ions from water, the apparatus        comprising:

a housing comprising:

-   -   an inlet to let water into the housing,    -   an outlet to let water out of the housing, and    -   a first and a second electrode connected to a power controller        configured to apply an electrical potential difference between        the first and the second electrodes;

a spacer between the first and second electrodes to allow water to flowin between the first and second electrodes, the spacer comprising apillar structure.

35. The apparatus according to clause 34, wherein the first and secondelectrodes each have a substantially flat surface and the pillarstructure is between the first and second electrodes to keep the firstand second electrodes at a substantially constant distance from eachother.36. The apparatus according to clause 35, wherein the pillar structureis sandwiched in between the flat surface of the first and secondelectrodes or a membrane of the first electrode and/or the secondelectrode.37. The apparatus according to any of clauses 34-36, wherein the pillarstructure is physically or chemically attached onto a surface of thefirst electrode and/or the second electrode or a membrane of the firstelectrode and/or the second electrode.38. The apparatus according to any of clauses 34-37, wherein the pillarstructure is, between the electrodes, substantially perpendicular to theflow direction.39. The apparatus according to any of clauses 34-38, wherein the spacercomprises a netting framework to keep pillars of the pillar structure ata substantially fixed distance from each other.40. The apparatus according to clause 39, wherein the netting frameworkis constructed and arranged to keep the longitudinal axis of the pillarstructure substantially perpendicular with respect to the flow directionof the water flowing between the first and second electrodes.41. The apparatus according to any of clauses 34-40, wherein the centerpart of the pillar structure is attached to a netting framework.42. The apparatus according to any of clauses 39-41, wherein the nettingframework and/or pillar structure creates movement of watersubstantially perpendicular to the flow direction of the water flowingbetween the first and second electrodes.43. The apparatus according to any of clauses 34-42, wherein the pillarstructure comprises a thicker middle portion in order to provide for anincreased flow resistivity in the center of a flow channel in betweenthe first and second electrodes.44. The apparatus according to any of clauses 34-43, wherein thethickness of the pillar structure decreases from the center of thepillar structure to an edge of the pillar structure.45. The apparatus according to any of clauses 34-44, wherein the pillarstructure is spherical, elliptical, rhombus, egg or ball shaped.46. The apparatus according to any of clauses 39-45, wherein the nettingframework is provided in the middle of a flow channel in between thefirst and second electrodes.47. The apparatus according to any of clauses 34-46, wherein the pillarstructure is made out of one piece extending over the full width of aflow channel between the first and second electrodes.49. A method of manufacturing an apparatus to remove ions from water,the method comprising:

providing a spacer comprising a pillar structure to a first electrode;and

providing a second electrode to the spacer.

50. The method according to clause 49, further comprising providing amembrane to the first electrode before the spacer is provided to thefirst electrode.51. The method according to clause 49 or clause 50, wherein providingthe spacer comprises attaching the pillar structure to the firstelectrode or the membrane.

It is to be understood that the disclosed embodiments are merelyexemplary of the invention, which can be embodied in various forms.Therefore, specific structural and functional details disclosed hereinare not to be interpreted as limiting, but merely as a basis for theclaims and as a representative basis for teaching one skilled in the artto variously employ the present invention in virtually any appropriatelydetailed structure. Furthermore, the terms and phrases used herein arenot intended to be limiting, but rather, to provide an understandabledescription of the invention.

The terms “a” or “an”, as used herein, are defined as one or more thanone. The term another, as used herein, is defined as at least a secondor more. The terms including and/or having, as used herein, are definedas comprising (i.e., not excluding other elements or steps). Anyreference signs in the claims should not be construed as limiting thescope of the claims or the invention. The mere fact that certainmeasures are recited in mutually different dependent claims does notindicate that a combination of these measures cannot be used toadvantage. The scope of the invention is only limited by the followingclaims.

1. An apparatus to remove ions from water, the apparatus comprising: ahousing; an inlet to let water into the housing; an outlet to let waterout of the housing; a first and second electrode connected to a powercontroller configured to apply an electrical potential differencebetween the first and second electrodes; and a spacer between the firstand second electrodes for to allow water to flow in between the firstand second electrodes, the spacer comprising a pillar structure.
 2. Theapparatus according to claim 1, wherein the first and second electrodeseach have a substantially flat surface and the pillar structure islocated between the electrodes to keep the electrodes at a substantiallyconstant distance from each other.
 3. The apparatus according to claim2, wherein the pillar structure is sandwiched in between the flatsurfaces of the first and second electrodes or a membrane of the firstor second electrode.
 4. The apparatus according to claim 1, wherein thepillar structure is physically or chemically attached onto a surface ofthe first or second electrode or a membrane on a surface of the first orsecond electrode.
 5. The apparatus according to claim 1, wherein thepillar structure is located between the electrodes perpendicular to theflow direction.
 6. The apparatus according to claim 1, wherein thespacer comprises a netting framework to keep pillars of the pillarstructure at a substantially fixed distance from each other.
 7. Theapparatus according to claim 6, wherein the netting framework isconstructed and arranged to keep the longitudinal axis of the pillarstructure substantially perpendicular with respect to the flow directionof the water flowing between the first and second electrodes.
 8. Theapparatus according to claim 1, wherein the center part of the pillarstructure is attached to a netting framework.
 9. The apparatus accordingto claim 6, wherein the netting framework and/or pillar structurecreates movement of water substantially perpendicular to the flowdirection of the water flowing between the first and second electrodes.10. The apparatus according to claim 1, wherein the pillar structurecomprises a thicker middle portion to provide for an increased flowresistivity in the center of a flow channel between the first and secondelectrodes.
 11. The apparatus according to claim 1, wherein thethickness of the pillar structure decreases from the center of thepillar structure to an edge of the pillar structure.
 12. The apparatusaccording to claim 1, wherein the pillar structure is spherical,elliptical, rhombus, egg or ball shaped.
 13. The apparatus according toclaim 6, wherein the netting framework is in the middle of a flowchannel.
 14. The apparatus according to claim 1, wherein the pillarstructure is made out of one piece extending over the full width of aflow channel between the first and second electrodes.
 15. A method ofmanufacturing an apparatus to remove ions from water, the methodcomprising: providing a spacer comprising a pillar structure to a firstelectrode; and providing a second electrode to the spacer.
 16. Themethod according to claim 15, further comprising providing a membrane tothe first electrode before providing the spacer to the first electrode.17. The method according to claim 15, wherein providing the spacercomprises attaching the pillar structure to the first electrode or amembrane.
 18. An apparatus to remove ions from water, the apparatuscomprising: a housing; an inlet to let water into the housing; an outletto let water out of the housing; a first and second electrode connectedto a power controller configured to apply an electrical potentialdifference between the first and the second electrodes; and a spacerbetween the first and second electrodes to allow water to flow inbetween the first and second electrodes, the spacer comprising a helicalstructure.
 19. The apparatus according to claim 18, wherein the firstand second electrodes each have a substantially flat surface at asubstantially constant distance from each other and the helicalstructure is sandwiched in between the flat surfaces of the first andsecond electrodes.
 20. The apparatus according to claim 18, wherein thehelical structure forces the water to twist along the helical structure.21. The apparatus according to claim 18, wherein the helical structureforces the water further away from the electrodes to a position closerto the electrodes.